Method of assembling inserts with precision looseness

ABSTRACT

In an illustrative embodiment, a limitedly radially slidable orifice element or insert is assembled within an aperture of a piston end cap of a hydraulic dashpot type of mounting unit for automotive vehicle bumpers. The orifice insert is assembled in the end cap by a method involving the forming of at least one radial flange in a crimping-like operation to tightly engage it and an opposite preformed flange with respective surfaces of the end cap, and subsequently reforming one of the flanges to displace the other a predetermined distance from its respective end cap surface affording precision clearance for relatively free sliding movement of the insert within the end cap.

StatesfPatent [191 Mccienanieiai;

, Jan. 15, 1974 METHOD OF ASSEMBLING INSERTS WITH PRECISION LOOSENESS[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 28, 1972 [2]] Appl. No.: 284,164

Gifford 29/512 UX 1,468,662 9/ 1 923 1,647,992 11/1927 1 1,909,4785/1933 2,087,969 7/1937 2,121,464 6/1938 Zagorski 251/365 2,462,138-2/1949 Spangenberg 29/437 X Primary Examiner-Charlie T. Moon Att0rneyW.E. Finken et al.

[57] ABSTRACT In an illustrative embodiment, a limitedly radiallyslidable orifice element or insert is assembled within an aperture of apiston end cap of a hydraulic dashpot type of mounting unit forautomotive vehicle bumpers. The orifice insert is assembled in the endcap by a method involving the forming of at least one radial flange in acrimping-like operation to tightly engage it and an opposite preformedflange with respective surfaces of the end cap, and subsequentlyreforming one of the flanges to displace the other a predetermineddistance from its respective end cap surface affording precisionclearance for relatively free sliding movement of the insert within theend cap.

I METHOD OF ASSEMBLING INSERTS WITH PRECISION LOOSENESS This inventionrelates to methods of assembly for self-retention of inserts withinapertures of members and more particularly to a method for assemblingsuch inserts with precision looseness permitting relatively free lateralshiftable movement of the insert within such aperture.

Prior methods of assembly for permanently attaching inserts withinapertured members have generally been directed to either quite firmengagement of the insert within the member, or indiscriminate loosenessof the insert arising from only partial rolling, crimping or likeformation ofa flange of the insert in a single step of the assemblyoperation. In certain instances, it is desirable to assemble such aninsert for permanent retention with but a slight yet precise clearancesufficient to permit relatively free lateral shifting of the insertwithin an oversized aperture of the apertured member; i.e., no grosslooseness. Such is particularly the case, for example, in the assemblyof an orifice element within the piston end cap of the disclosedillustrative embodiment of a hydraulic dashpot bumper mount unit forautomobile bumper systems. There, the orifice element is situated withinan oversized aperture in the piston end cap of a piston tube assemblytelescopically related with a cylinder tube having affixed thereto ametering rod which projects through the fluid flow aperture of theorifice element for controlled metering of fluid flow during telescopingof the bumper mount unit. To accommodate limited misalignment normallyencountered in manufacture and assembly of the several parts of thebumper mount unit, the orifice element should be free to center itselfwith the metering rod through the provi sion of room for lateralshifting of the element and with a precise clearance between theretaining flanges of the orifice element from the juxtaposed surfaces ofthe end cap. Such clearance should not be indiscriminately loose to anyextent allowing uncontrolled and unpredictable fluid flow through suchclearance space remote from the metering rod.

In accordance with these objectives, the present invention features amethod of assembly of inserts within apertured members wherein flangesare formed on the insert for juxtaposition to opposite walls of themember adjacent the edge of the aperture, the method involvingreformation of at least one of the flanges from an initially tightengagement of the flanges with the member to a displaced condition ofthe insert wherein precise clearance is provided affording the desiredfree lateral or radial shifting movement of the insert.

Another feature of this invention is in the formation of such flangeswith precise clearance as part of an automated process such as involvedin transfer presses so as to provide the required precision assemblywithout sacrificing speed or economy of manufacture.

These and other features and advantages of the invention will be readilyapparent from the following specification and from the drawings wherein:

FIG. 1 illustrates an assembled article realized by the process of thisinvention and shown in the illustrative environment of an automotivehydraulic dashpot type bumper mount unit;

HO. 2 is a view, partially broken away, illustrating an initial step inthe assembly method of this invention;

FIG. 3 is a view similar to FIG. 2 showing completion of a nextsubsequent step;

FIG. 4 is another similar view illustrating a further subsequent step;

FIG. 5 is another similar view showing the insert assembly completed;and

FIG. 6 is a partially broken away perspective view illustrating thefinished article.

Referring particularly to FIG. 1 of the drawings, there is shown ahydraulic dashpot vehicle bumper mount unit, disclosed generally as 10,which incorporates an orifice element and piston end cap assembled inaccordance with the method of this invention. For details of the bumpermount unit, its operation and its application within the bumper systemof an automotive vehicle, reference should be had to Jackson et al, USSer. No. 91,008 filed Nov. 19, 1970, now US. Pat. No. 3,700,273, andassigned to the assignee of the present invention. Generally, however,the bumper unit comprises telescopically arranged cylinder tube andpiston tube subassemblies 12 and 14 respectively. Cylinder tube assembly12 includes an outer tube or vessel 16 having secured thereto a forwardflange 18 at one end and a mounting stud 20 at the opposite end suitablefor attachment to spaced flange structures 22 which project from, forexample, the sides of the longitudinally extending forward frame railportions or horns of the vehicle.

Telescopically received within cylinder tube 16 with relatively closefit is the piston tube assembly 14, which latter has fixedly attached tothe outer end thereof the usual vehicle bumper or impact face bar 24. Itwill be understood that at least two bumper mount units 10 are employed,one at either side of the vehicle frame, for attachment to respectiveend portions of the face bar 24. The attachment to the face bar is bestafforded by a pivot structure such as illustrated at 26 which mayinclude an elastomeric bushing between flanges attached respectively tothe piston tube assembly and the face bar affording limited rotation ona vertical axis between such flanges as can arise from corneringimpactson the face bar tending to displace one end of the same relativeto the vehicle a greater distance than the opposite end of the face bar.

The piston tube assembly is relatively closely slidably fitted withincylinder tube 16 by a pair of longitudinally spaced bearings 28 and 30deriving from the cylinder tube assembly firm structural support for theface bar during all manner of operating conditions of the vehicle andutilizing material antifriction properties such as available fromglass-filled nylon or the like to present substantially no impediment totelescoping of the piston tube subassembly inwardly of the cylinder tubeduring impact. Such telescoping occurs as between a normal extendedposition, as shown, and any of a plurality of inwardly displacedpositions carrying a piston end cap 32, which is welded or otherwisesecured to the end of piston tube 34, toward the inner end wall of thecylinder tube 16. Such displacement of course changes the relativevolume of two working chambers 36 and 38 of the bumper mount unit andforces hydraulic fluid such as oil which is contained therein to flowthrough an orifice element 40 of mild or low carbon steel. Workingchamber 36 may include an annular volume 42 surrounding the piston tube34 and closed at the forward end of the unit by a sealing O-ring 44backed up by the bearing 28. To firmly support the piston tube assemblyon the cylinder tube assembly in the extended relationship shown, a stopring 46 affixed to the piston tube 34 and supporting the bearing 28 hasa generally frustoconical surface tightly engageable with acomplementary crimp surface 48 at the end of the cylindertube 16.

Within the piston tube 34 is a variable volume working chamber 38 whichis closed at one side by a gas piston 50 sealed by an O-ring to theinner surface of piston tube 34 to contain a pressurized volume ofnitrogen or other inert gas. Such gas is subject to compression bypiston 50 during impact caused telescoping within bumper mount unit 10,thereby to act as a spring which will return the unit to its normalextended condition, as shown, upon release of the impact force on facebar 24.

A metering rod 52 affixed generally on the centerline of the unit to theend wall of cylinder tube 16 projects into the orifice or center openingof orifice element 40 and has flats 54 thereon providing controlled flowarea between the periphery of the metering rod and the inner lip 66 ofthe orifice element. Such flats 54 are of varying depth to providevarying flow area as the piston tube assembly telescopes inwardlywhereby to provide a tailored generally constant pressurization forcewithin the unit as the velocity of telescoping varies during impact.

Because of limited amounts of manufacturing tolerance misalignmentpossible between the metering rod 52 and the axis of the piston tubesubassembly during telescoping, it is desirable to permit orificeelement 40 to float or displace radially a limited distance to maintaina uniform operating relationship with the metering rod as the bumpermount unit is telescoped.

Referring to FIG. 6, a preferred construction for the assembly of partsincluding piston end cap 32 and orifice element 40 is shown. Piston endcap is apertured centrally at 58 to have inserted therein the orificeelement. The opposite surfaces or walls of the piston end cap designated60 and 62 are preferably planar adjacent such aperture 58. The orificeelement 40 includes an annular wall 64 terminating in the inner sharporificing edge 66, and formed integrally with annular wall 64 areopposed flanges 68 and 70. As indicated in FIG. 6, slight looseness ofthe inserted orifice element 40 is provided by a precise clearanceillustrated by the space between flange 70 and piston end cap wall 60.Further, the outer dimension of the annular wall 64 is predeterminedlysmaller than the aperture 58. This latter dimensional difference ispredetermined to accommodate the maximum axial misalignment expectedbetween the metering rod 52 and the axis of piston tube assembly 14 onwhich the aperture 58 is centered. The clearance gap between flange 70and wall 60 is precisely predetermined so that, while the two flanges 68and 70 positively retain the orifice element, they impose no substantialfrictional resistance to self-induced centering or alignment of theorifice element relative to the metering rod during telescoping of thebumper mount unit 10. The clearance gap shown at flange 70 should beheld closely so that there is no possibility of significant fluid flowat the outside of the orifice element 40 around its flanges and throughthe clearance space between annular wall 64 and aperture 58 causingunpredictable fluid flow conditions during telescoping of the unit 10 orrebound thereof from the gas spring. A typical desired clearance spaceis .005 inches. It is to be appreciated that the clearance space shownat 70 in FIG. 6 is merely illustrative and in practice representslooseness between flange 68 and wall 58 as well. Indeed, with suchclearance gap, the orifice element will shift axially of the end cap toabut one flange or the other thereon depending on the direction of themoderate pressure differentials normally experienced either side of theend cap during telescoping of unit 10.

Referring to FIG. 2, there is illustrated an initial step in the methodof assembly and fabrication of theassembled article of FIG. 6. Pistonend cap 32 is firmly seated on a fixture plate 72 which may be part ofan automated transfer press or the like. Such plate rests on a support74 of the press, which latter contains a tool support or reaction member76 within a bore 78 of the fixture plate 72. The upper surface of toolsupport 76 is recessed from a supporting surface 80 of plate 72 aprecise distance to accept the thickness of a preformed flange of theorifice element 40. Such orifice element is shown in a blank form 40a,in FIG. 2 wherein it includes the preformed flange, which may be flangeas seen in FIG. 6, as well as a generally frustoconical annular wall 40bupstanding from flange 70 and which has been inserted within aperture 58of the end cap. It is to be noted that the upper surface of the toolsupport is planar to press generally planar flange 70 against end capwall 60 during the press operation. The next step utilizes a tool 82affixed within tool holder 84 attached to a movable ram of the press.Tool 82 includes an annular work engaging surface conformation 86. Thedepth of such conformation is indicated in FIG. 2 by the distance X.Downward motion of tool 82 in its holder engages the work engagingconformation 86 with the upper annular lip of upstanding wall 40b anddeforms and stretches the same into a crimped or curled flange 400, thecompletion of this step being illustrated in FIG. 3. The intermediatestate of the assembled article following lifting of tool 82 is seen inFIG. 4. The material upsetting curls flange 400 into engagement firmlywith planar surface 58 but generally only at the outer edge or lip ofsuch flange. The orifice element 40a has both its flanges thus firmlyengaged with the piston end cap.

Following lifting of the tool 82, the assembled article in itsintermediate state is then reconditioned within the press to thesituation or station illustrated in FIG. 4 wherein the piston end capstill rests on a supporting surface in its fixture 72 but all support isremoved from the lower flange 70 of the orifice element. Flange 400 isthen restruck by another tool 88 attached to a movable ram by a toolholder 90. Tool 88 includes a work engaging surface 92 of planarconformation which is recessed a distance Y from a stop or referencesurface 94 of the tool holder 90. The completion of this restrik ing ofcurled flange 40c is illustrated in FIG. 5 where it is seen that thereference surface 94 limits the extent of the restriking motion of tool88 by its engagement with piston end cap surface 58. With the piston endcap being firmly supported on the press fixture support 74, and the factthat the orifice element blank 40a is unsupported other than at the edgeor lip of flange 400, work engaging surface 92 further upsets andreforms the material of such flange to the condition shown in FIG. 5.There, the height of flange 40c has been partially uncurled or flattenedabout the engaged outer lip thereof and the flange 70 has been displacedfrom end cap surface 60 a precise distance. This precise distance iscontrolled by the depth of recess between work engaging surface 92 andreference surface 94 indicated by distance Y. Thus, in effect, theamount of clearance established at the flange 70 as shown in FIG. 5 is afunction of the difference between distances X and Y.

It is of course to be appreciated that the specific tools and steps ofoperation illustrated and described in the foregoing may be consideredin some respects peculiar to the finished shape of orifice element 40 asseen in FIG. 6. The generalized approach to precision looseness of aninsert in an apertured member is adaptable to other shapes of flangesfor the insert. For example, where the insert need have no sharp orificeedge 66, the planar shape of flange 70 may be discarded. It may be, forexample, preformed in a curl similar to the flange 40c and the toolsupport 76 may be suitably shaped to accept such a flange and support itduring the initial press steps of FIGS. 2 and 3. The steps of FIGS. 4and 5 may then involve restriking of either one of such curled flanges.Other departures or modifications from the generalized approachdisclosed herein may also be utilized.

Having thus described the invention, what is claimed I. In a method offorming an assembly including an apertured member and an insert in theaperture thereof having opposite flanges juxtaposed to respective wallsof said member at the edge of the aperture, said flanges having apredetermined precise clearance from said walls, the steps comprising,inserting within said aperture of said member an insert blank having apreformed one of said flanges and an upstanding annular wall connectedwith said one flange, striking said upstanding wall with a tool whilesupporting said preformed flange firmly engaged in at least a localregion thereof with its respective wall of said member to bend an upperportion of said annular wall into a flange firmly engaged in only alocalized region thereof with the opposite wall of said member, andrestriking a non-engaged portion of one of said flanges with a toolwhile said member is supported and the other flange is unsupported tobend said restruck flange toward its respective wall and remove theopposite flange from its respective wall of said member to a preciseextent providing the predetermined clearance required between theflanges of said insert and the respective walls of said member.

2. In a method of forming an assembly including an apertured member andan insert in the aperture thereof having opposite flanges juxtaposed torespective generally planar walls of said member at the edge of theaperture, said flanges having a predetermined precise clearance fromsaid walls, the steps comprising, inserting within said aperture of saidmember an insert blank having a preformed generally planar one of saidflanges and an upstanding annular wall connected with said one flange,striking said upstanding wall with a tool while supporting said oneflange firmly engaged with its respective wall of said member to bend anupper portion of said annular wall into a curled flange firmly engagedin only an outer edge region thereof with the opposite wall of saidmember, and restriking a nonengaged portion ofsaid curled flange with atool while the member is supported and said one flange is unsup-- portedto further bend said curled flange toward its respective wall and removesaid one flange from its respective wall of said member to a preciseextent providing the predetermined clearance required between theflanges of said insert and the respective walls of said member.

3. In a method of forming an assembly including an apertured member andan insert in the aperture thereof having opposite flanges juxtaposed torespective walls of said member at the edge of the aperture, saidflanges having a predetermined precise clearance from said walls, thesteps comprising, inserting within said aperture of said member aninsert blank having a preformed one of said flanges and an upstandingannular wall connected with said one flange, striking said upstandingwall with a tool while supporting said preformed flange firmly engagedin at least a local region thereof with its respective wall of saidmember to bend an upper portion of said annular wall into a flangefirmly engaged in only a localized region thereof with the opposite wallof said member, supporting said member, removing support from one ofsaid flanges and restriking a nonengaged portion of the other of saidflanges with a tool which has a reference surface engageable with saidmember and a flange striking surface recessed from said referencesurface a predetermined amount related to said predetermined clearanceto bend said restruck flange toward its respective wall and remove theopposite flange from its respective wall of said member to a preciseextent limited by engagement of said reference surface with said member,thereby to provide the predetermined clearance required between theflanges of said insert and the respective walls of said member.

4. In a method of forming an assembly including an apertured member andan insert in the aperture thereof having opposite flanges juxtaposed torespective generally planar walls of said member at the edge of theaperture, said flanges having a predetermined precise clearance fromsaid walls, the steps comprising, inserting within said aperture of saidmember an insert blank having a preformed generally planar one of saidflanges and an upstanding annular wall connected with said one flange,striking said upstanding wall with a tool while supporting said oneflange firmly engaged with its respective wall of said member to bend anupper portion of said annular wall into a curled flange firmly engagedin only an outer edge region thereof with the opposite wall of saidmember, supporting said member, removing support from said one flangeand restriking a nonengaged portion of said curled flange with a toolwhich has a reference surface engageable with said member and a flangestriking surface recessed from said reference surface a predeterminedamount related to said predetermined clearance to further bend saidcurled flange toward its respective wall and remove said other flangefrom its respective wall of said member to a precise extent limited byengagement of said reference surface with said member, thereby toprovide the predetermined clearance required between the flanges of saidinsert and the respective walls of said members.

1. In a method of forming an assembly including an apertured member andan insert in the aperture thereof having opposite flanges juxtaposed torespective walls of said member at the edge of the aperture, saidflanges having a predetermined precise clearance from said walls, thesteps comprising, inserting within said aperture of said member aninsert blank having a preformed one of said flanges and an upstandingannular wall connected with said one flange, striking said upstandingwall with a tool while supporting said preformed flange firmly engagedin at least a local region thereof with its respective wall of saidmember to bend an upper portion of said annular wall into a flangefirmly engaged in only a localized region thereof with the opposite wallof said member, and restriking a non-engaged portion of one of saidflanges with a tool while said member is supported and the other flangeis unsupported to bend said restruck flange toward its respective walland remove the opposite flange from its respective wall of said memberto a precise extent providing the predetermined clearance requiredbetween the flanges of said insert and the respective walls of saidmember.
 2. In a method of forming an assembly including an aperturedmember and an insert in the aperture thereof having opposite flangesjuxtaposed to respective generally planar walls of said member at theedge of the aperture, said flanges having a predetermined preciseclearance from said walls, the steps comprising, inserting within saidaperture of said member an insert blank having a preformed generallyplanar one of said flanges and an upstanding annular wall connected withsaid one flange, striking said upstanding wall with a tool whilesupporting said one flange firmly engaged with its respective wall ofsaid member to bend an upper portion of said annular wall into a curledflange firmly engaged in only an outer edge region thereof with theopposite wall of said member, and restriking a nonengaged portion ofsaid curled flange with a tool while the member is supported and saidone flange is unsupported to further bend said curled flange toward itsrespective wall and remove said one flange from its respective wall ofsaid member to a precise extent providing the predetermined clearancerequired between the flanges of said insert and the respective walls ofsaid member.
 3. In a method of forming an assembly including anapertured member and an insert in the aperture thereof having oppositeflanges juxtaposed to respective walls of said member at the edge of theaperture, said flanges having a predetermined precise clearance fromsaid walls, the steps comprising, inserting within said aperture of saidmember an insert blank having a preformed one of said flanges and anupstanding annular wall connected with said one flange, striking saidupstanding wall with a tool while supporting said preformed flangefirmly engaged in at least a local region thereof with its respectivewall of said member to bend an upper portion of said annular wall into aflange firmly engaged in only a localized region thereof with theopposite wall of said member, supporting said member, removing supportfrom one of said Flanges and restriking a nonengaged portion of theother of said flanges with a tool which has a reference surfaceengageable with said member and a flange striking surface recessed fromsaid reference surface a predetermined amount related to saidpredetermined clearance to bend said restruck flange toward itsrespective wall and remove the opposite flange from its respective wallof said member to a precise extent limited by engagement of saidreference surface with said member, thereby to provide the predeterminedclearance required between the flanges of said insert and the respectivewalls of said member.
 4. In a method of forming an assembly including anapertured member and an insert in the aperture thereof having oppositeflanges juxtaposed to respective generally planar walls of said memberat the edge of the aperture, said flanges having a predetermined preciseclearance from said walls, the steps comprising, inserting within saidaperture of said member an insert blank having a preformed generallyplanar one of said flanges and an upstanding annular wall connected withsaid one flange, striking said upstanding wall with a tool whilesupporting said one flange firmly engaged with its respective wall ofsaid member to bend an upper portion of said annular wall into a curledflange firmly engaged in only an outer edge region thereof with theopposite wall of said member, supporting said member, removing supportfrom said one flange and restriking a nonengaged portion of said curledflange with a tool which has a reference surface engageable with saidmember and a flange striking surface recessed from said referencesurface a predetermined amount related to said predetermined clearanceto further bend said curled flange toward its respective wall and removesaid other flange from its respective wall of said member to a preciseextent limited by engagement of said reference surface with said member,thereby to provide the predetermined clearance required between theflanges of said insert and the respective walls of said members.